In modern aircrafts, the passengers are serviced by the crew only. Flight attendants deliver meals and beverages to the passengers on trays that are transported to the respective row of seats with the aid of trolleys. These meals are prepared or heated and assembled in galleys or on-board kitchens. The crew needs to begin with the service preparations immediately after take-off and deliver the heavy trolleys to the passengers, if applicable, while the aircraft is still climbing. This service concept is associated with high expenditures and a lack of flexibility for the passengers because each passenger is dependent on being served directly by a crew member.